It is often quoted that “horsepower sells cars”. A stronger car with more horsepower is generally preferred over a weaker alternative with less horsepower. Horsepower is a unit of measure often cited in the automotive industry especially in high performance cars. The definition of one horsepower is 33,000 foot-pounds per minute. Horsepower is an important engine parameter but an engine's horsepower is not directly measured. Horsepower is derived from other measurable forces.
One method of determining horsepower measures the torque produced by an engine and converts the torque to horsepower by the equation HP=Torque×R.P.M±5252. To directly measure torque, a dynamometer may be coupled to an engine. The dynamometer places a load on the engine and measures the amount of torque that the engine can produce against the load.
A typical dynamometer comprises a rotor and housing. A load is placed on the engine by some braking means on the rotor. Different braking means include dry friction brake, hydraulic brakes, electromagnetic brakes. Modern dynamometer may include processors to convert the measured torque to horsepower.
One disadvantage of measuring torque using a dynamometer is the cost. An engine dynamometer may cost upwards of $50,000 U.S.D. Furthermore, coupling an engine to a dynamometer may be labor and time intensive. Attaching the engine to the rotor of a dynamometer may require the removal of the engine or at least partial disassembly to connect the engine to the dynamometer rotor.
Although horsepower sells cars, in some sense, torque is more important than horsepower. Torque is what a actually driver feels during acceleration, while horsepower is an esoteric arbitrary measurement. Horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only coincide at 5252 rpm, where horsepower and torque are equal in magnitude.
Hot rod enthusiasts are especially interested in measuring the torque of their engines. Hot rod enthusiasts measure torque because, from a driver's perspective, a car will accelerate at a rate that matches its torque curve. A car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Peak torque is a “sweet spot” for performance.
What is needed is an onboard method and device for measuring torque generated by an automotive engine. What is needed is a method of measuring automotive engine torque without needing to remove the engine from the car as required by a dynamometer.